1. Field of the Invention
This invention relates to improvements in line protectors of the type that are located between equipment to be protected and the outside lines which arrive at the site where the equipment is located and use solid state overvoltage arresters.
2. Description of the Prior Art
There has been a trend in the telecommunications industry to use solid state devices as overvoltage arresters in place of either gas tubes or carbon elements. Carbon element and gas tube surge arresting devices rely on an arc discharge to initiate protection. This discharge may cause degradation in the performance of the device which, over time, creates different types of in-service problems. Those problems can range from short circuits to various forms of low voltage operation and current leakage. The degradation can also cause disturbances on the telephone line which are noticeable to the subscriber, who brings them to the attention of the operating company providing the service. The operating company must then have its personnel investigate such "trouble" reports, resulting in the expenditure of both time and money.
Solid state overvoltage arresters, on the other hand, provide noise-free transmission and have a greatly reduced maintenance and longer service life as compared to the carbon element or gas tube surge arresting devices. Therefore, it is desirable to use, wherever possible, solid state overvoltage devices in place of carbon element or gas tube devices. It is further desirable to be able to insert such solid state devices directly in existing line protector units in place of either the carbon element or gas tube surge arresting devices presently used in those units.
One example of such a line protector is shown in U.S. Pat. No. 4,958,253 entitled "Line Protector For A Communications Circuit" (hereinafter "the '253 patent") which is assigned to the same assignee as is the present invention. The line protector shown and described in the '253 patent uses a solid state overvoltage arrester and has a solid conductive pedestal between one electrode of the arrester and the closed end of the cup which contains the arrester. The closed end of the cup is in contact with the ground pin of the protector. The pedestal provides the conductive path between the arrester and the cup upon the occurrence of a transient overvoltage condition on either of the two wires in the telephone line pair to which the protector is connected.
It is desirable to reduce the cost of the line protector described in the '253 patent. The cost can be reduced if a nonsolid pedestal can be used in place of the solid pedestal used in the protector of the '253 patent.
Line protectors are subject to a number of standard tests. One such test is the drop test wherein the protector is dropped from a predetermined height, typically five (5) feet, onto a hard surface such as a concrete floor. The drop test is meant to simulate the inadvertent dropping of a line protector by an individual such as a telephone company craftsperson. It has been found in the protector of the '253 patent that the solid state arrester may be damaged during the drop test. Therefore, the protector of the '253 patent may not always pass the drop test.
I believe the main reason that the protector of the '253 patent does not always pass the drop test is the mass of the solid conductive pedestal. I also believe that the solid conductive pedestal may not be flexible enough. Therefore, it is desirable to reduce the mass of the solid pedestal by replacing it with one that is nonsolid. The nonsolid pedestal also reduces the cost of the protector. In addition, it is further desirable at the same time to provide flexibility in the pedestal to overcome any possibility that the nonsolid pedestal might damage the arrester during the drop test.